Work, from our lab and others, has established that the beneficial, anti-cancer function of the p16INK4a tumor suppressor mechanism also untowardly contributes to mammalian aging. In this model, the age-associated expression of p16INK4a compromises organismal fitness by limiting the regeneration and repair of certain self-renewing compartments. In support of this hypothesis, recent data from our lab and collaborators has shown that p16INK4a-deficient animals demonstrate a resistance to certain aging phenotypes in pancreatic -cells, neural stem cells and hematopoietic stem cells, while transgenic animals expressing excess p16INK4a demonstrate an accelerated functional decline with aging in these compartments. Additional support for this model has come from recent human genome-wide and candidate association studies which have linked single nucleotide polymorphisms near the CDKN2a locus, which encodes p16INK4a, to human age-associated conditions such as frailty, type 2 diabetes and atherosclerotic disease (myocardial infarction, ischemic stroke and abdominal aortic aneurysm). In the renewal of this proposal, we seek to extend these prior observations to further enhance our understanding of how p16INK4a influences mammalian aging. In specific aim I, we propose to further define the role of p16INK4a in pancreatic -cell aging using a novel p16INK4a-conditional allele generated in our lab. In specific aim II, we will further study the role of p16INK4a in a murine model of atherosclerosis using germline and conditional p16INK4a-deficient mice. In specific aims III and IV, we will focus on the role of p16INK4a in lymphocyte aging. In aim III, we will characterize T- and B-cell number and function in mice harboring somatic inactivation of p16INK4a in these tissues. In aim IV, we will study the expression of p16INK4a in human T-cells with aging and after exposure to age-promoting stimuli such as cytotoxic chemotherapy. Through these approaches, we will further delineate the contribution of p16INK4a to age-associated phenotypes such as type 2 diabetes, atherosclerosis and immune dysfunction in humans in mice.